Sedimentary Characteristics And Burial Factors Of Polycyclic Aromatic Hydrocarbons In Dianchi Lake Sediments

With the rapid economic development,the process of industrialization and urbanization has accelerated,and industrial and agricultural production activities discharge a large amount of waste,which has a serious impact on the environment.As a relatively closed and independent ecosystem,lakes have a long renewal cycle of water bodies.Once pollutants enter the lake,it will be difficult to manage and remove them.Lake governance has become an important subject of scientific research today.This paper mainly takes Dianchi Lake in Yunnan Province as the research object,collecting surface and columnar sediment samples of Dianchi Lake to determine the particle size,organic carbon(TOC),total nitrogen(TN),carbon and nitrogen isotopes(?¹³C,?¹⁵N),n-alkanes(n-Alkanes)and polycyclic aromatic hydrocarbons(PAHs)and other indicators are analyzed to explore the source of organic matter in the sediments of Dianchi Lake and the burial characteristics of PAHs.And further analyze the source characteristics and particle size,TOC and the influence of internal and external organic matter on the burial of PAHs.The main conclusions are as follows:(1)The particle size distribution in the surface and core sediments of Dianchi Lake is dominated by silt,followed by clay and sand.The particle size in the sediments is very poorly sorted;the particle size frequency distribution curve of the sedimentary core changes from single-peak to double-peak,indicated the source of sediments in Dianchi Lake has changed.(2)TOC and TN contents in surface sediments of Dianchi Lake are higher in the north than in the south,and the high value area appears in Caohai area in the north of Dianchi Lake.The TOC and TN contents in the sedimentary core have increased rapidly since the 1970s,and the primary productivity of Dianchi Lake has been continuously improved,and the watershed environment has begun to degenerate.The sources of organic matter in Dianchi Lake sediments were analyzed by using C/N ratio,?¹³C,?¹⁵N isotope and n-Alkanes.The historical changes of organic matter sources in Dianchi Lake core sediments changed from internal sources to internal and external mixed sources,while the surface sediments were mainly internal and external mixed sources.(3)The PAHs pollution in the sediments of Dianchi Lake is at a moderate level.In terms of spatial distribution,the most severely polluted area is Caohai,which has many sources and inputs.The environmental closure of the lake area is not conducive to the dilution of pollutants,resulting in serious lake pollution.In the sediment core,the historical trend of PAHs concentration increased first and then decreased.It began to increase rapidly in the 1970s and began to decline after the 21st century;its composition is dominated by the 3 and 4 rings,and with the increase of the deposition depth,the contribution of HMW-PAHs continues to increase.The PAHs in the mid-to-high range mainly come from the high-temperature combustion emissions of fossil fuels,and the change in the contribution percentage represents the increasing impact of human activities on the environment.(4)According to PMF model analysis,the sources of PAHs in Dianchi Lake sediments mainly include petrogenic,biomass combustion,coal combustion,gasoline and diesel combustion and traffic emission.Through the analysis the changes of historical sources of PAHs in Dianchi Lake sediments,it was mainly petrogenic before 1940s.It was the source of biomass combustion in the 1940s and 1960s;In1980s,coal combustion was the main source,and the contribution of traffic emission sources began to increase.In 1990s,traffic emission became the main source.In modern sediments,PAHs mainly come from the combustion of fossil fuels,and the contribution of petrogenic is low,only 12.6%.(5)Correlation analysis of TOC,particle size,internal and external organic matter and PAHs in Dianchi Lake sediments shows that PAHs burial in Dianchi Lake sediments is significantly affected by TOC and external organic matter.With the increase of PAHs molecular weight,the influence of TOC and exogenous organic matter on PAHs is more significant,and the influence of particle size on PAHs is mainly controlled by the distribution of TOC in particle size.In summary,the distribution characteristics of PAHs in sediments are mainly affected by their sources.Increased use of fossil fuels has changed the burial amount and structure of PAHs in sediments.TOC and exogenous organic matter can promote the burial of PAHs in sediments.